Biochemical Markers Reflecting Thyroid Function in Athyreotic Patients on Levothyroxine Monotherapy

Abstract

Background: Some investigators reported that among athyreotic patients on levothyroxine (LT4) monotherapy following total thyroidectomy, the patients with normal serum thyrotropin (TSH) levels had mildly low serum free triiodothyronine (fT3) levels, whereas the patients with mildly suppressed serum TSH levels had normal serum fT3 levels, and the patients with strongly suppressed serum TSH had elevated serum fT3 levels. The objective of the present study was to clarify which of these three patient groups is closer to their preoperative euthyroid condition.Methods: A total of 133 consecutive euthyroid patients with papillary thyroid carcinoma who underwent a total thyroidectomy were prospectively studied. The patients' serum levels of lipoproteins, sex hormone-binding globulin, and bone metabolic markers measured preoperatively were compared with the levels measured at postoperative LT4 therapy 12 months after the thyroidectomy.Results: The postoperative serum sex hormone-binding globulin (p < 0.001) and bone alkaline phosphatase (p < 0.01) levels were significantly increased in the patients with strongly suppressed TSH levels (≤0.03 μIU/mL). The postoperative serum low-density lipoprotein cholesterol levels were significantly increased (p < 0.05), and the serum tartrate-resistant acid phosphatase-5b levels were significantly decreased (p < 0.05) in the patients with normal TSH (0.3 < TSH ≤5 μIU/mL). In the patients with mildly suppressed TSH (0.03 < TSH ≤0.3 μIU/mL) and fT3 levels equivalent to their preoperative levels, all metabolic markers remained equivalent to their preoperative levels.Conclusions: The serum biochemical markers of thyroid function in patients on LT4 following total thyroidectomy suggest that the patients with mildly suppressed TSH levels were closest to euthyroid, whereas those with normal TSH levels were mildly hypothyroid and those with strongly suppressed TSH levels were mildly hyperthyroid. These data may provide novel information on the management of patients following total thyroidectomy for thyroid cancer or benign thyroid disease.

The role of functional thyroid capacity in pituitary thyroid feedback regulation

“…17,18 After thyroidectomy, in the same patient treatment with levothyroxine (LT4) does not restore FT3 concentrations to the preoperative level at comparable TSH concentrations. 33,34 The impaired equilibria have been well recognised, being also associated with patient complaints during follow-up in LT4treated patients with thyroid carcinoma. 33,34 The impaired equilibria have been well recognised, being also associated with patient complaints during follow-up in LT4treated patients with thyroid carcinoma.…”

“…32 Nor does it raise FT3 to levels observed in the healthy population when TSH returns into the reference range. 22,[33][34][35][36][37] Here, we explored the potential role of functional thyroid capacity in thyroid-pituitary regulation. 22,[33][34][35][36][37] Here, we explored the potential role of functional thyroid capacity in thyroid-pituitary regulation.…”

“…46 Serum FT3 concentrations oscillate-as physiologically observed-only when including intrathyroidal T3 secretion. 17,18,21,33 Consequently, measurement of pituitary TSH is not merely a reflective mirror image of thyroid hormone status. Sensitivity of TSH to functional thyroid capacity increases with decreasing GT values, 46 explaining wide fluctuations in TSH concentrations in patients with subclinical hypothyroidism.…”

Persistent hypothyroid symptoms in a patient with a normal thyroid stimulating hormone level

“…Although sex hormone-binding globulin, cholesterol levels, and bone markers are generally considered to be relatively insensitive measures of thyroid status compared with TSH levels, a recent study comparing these measures in patients pre-thyroidectomy and post-thyroidectomy showed that these measures were best normalized in patients with mildly suppressed TSH values in the range of <0.03-≤0.3 mIU/L (17). If confirmed, this could suggest that TSH alone may not provide sufficient insight into thyroid status.…”

Thyroid Hormone Replacement – a Counterblast to Guidelines*

“…5 Recently it has been shown that, in thyroidectomised patients, it is necessary to give suffi cient LT4 to achieve a low serum TSH if preoperative concentrations of serum T3 and thyroxine (T4) are to be restored. 6 National Health and Nutrition Examination Survey data have revealed that prescribing a dose of LT4 which restores serum TSH to its somewhat wide reference range is associated with lower serum T3 and lower T3:T4 ratios than euthyroid individuals not taking LT4. These biochemical disadvantages were associated with adverse objective and subjective parameters, such as increased body mass index, lipid profi le and feelings of poor health.…”